Deformations

Displacements with respect to a reference coordinate system may be physically observed, calculated, or measured (at least on the surface) for a deformed elastic body. Each displacement may be considered to have two components, one of which is due to relative movements or distortions within the body and the other which is uniform throughout the body, so-called rigid body motion. The relationships between the displacements and the corresponding internal distortions are known as the kinematic or the strain-displacement equations of the theory of elasticity and may take several forms depending on the expected magnitude of the distortions and displacements.